Optical packet tray router

ABSTRACT

An optical packet tray router is disclosed that manipulates a signal wavelength as the fundamental control mechanism. The disclosed optical packet tray router aggregates one or more packets in a packet tray for transmission over a network. The header information associated with each packet is used to route each packet to the appropriate destination channel and to make timing decisions. A wavelength server generates optical control wavelengths in response to the timing decisions. A generated optical control wavelength is used to adjust the wavelength of a given packet tray and thereby introduce a wavelength selective delay to the packet tray to align packet trays or to shift one or more packet trays to avoid a collision. The wavelength of the packet tray is converted to a control wavelength corresponding to an identified delay, irrespective of the initial channel upon which the packet tray was received. At the output stage of the packet tray router, the packet tray wavelength can be converted to any desired output channel wavelength.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is related to U.S. patent applicationentitled “Method and Apparatus for Temporally Shifting One or MorePackets Using Wavelength Selective Delays,” (Attorney Docket NumberBeacken 7), filed contemporaneously herewith and incorporated byreference herein.

FIELD OF THE INVENTION

[0002] The present invention relates to optical communication networksand, more particularly, to optical devices for routing multi-wavelengthoptical signals.

BACKGROUND OF THE INVENTION

[0003] Many innovations for optical communication systems have involvedthe manner in which light waves are switched and manipulated. In manyoptical transmission applications, it is necessary to perform one ormore of the following actions on light: switching, wavelengthconversion, attenuation, waveform amplification/reshaping/retiming(1R/2R/3R), routing to different locations or manipulating the phase orpolarization of light. Such actions are critical for realization of theoptical networks that are the foundation of global communicationssystems.

[0004] Optical communication systems increasingly employ wavelengthdivision multiplexing (WDM) techniques to transmit multiple informationsignals on the same fiber, and differentiate each user sub-channel bymodulating a unique wavelength of light. WDM techniques are being usedto meet the increasing demands for improved speed and bandwidth inoptical transmission applications. In optical communication networks,such as those employing WDM techniques, individual optical signals areoften selectively routed to different destinations. Thus, a highcapacity matrix or cross-connect switch is often employed to selectivelyroute signals through interconnected nodes in a communication network.

[0005] At the heart of these cross-connect switches is the singleswitching unit. Electronic optical switches first convert an opticalsignal into an electrical signal to perform the switching and thenconvert the electrical signal back into optical signals. Theseconversions are very expensive and the switches are complex to managebut allow considerable flexibility. As networks grow and become dense,however, electronic switches become increasingly expensive and harder tofabricate.

[0006] Therefore, optical switches that operate directly on the lightwave are favorable. Optical switches are often realized in opticalwaveguides that can be manufactured with low cost and enable easymultiplexing and de-multiplexing of the WDM signal using waveguidegrating routers (WGR). For a detailed discussion of waveguide gratingrouters, such as those composed of optical star couplers and wavelengthdependent beam forming, see U.S. Pat. No. 4,904,042 to Dragone.

[0007] Currently available optical switches, however, allocate an entirewavelength to each packet in order to permit wavelength selectiverouting. Wavelengths that can be exploited for optical communicationsare finite in number and expensive to provision. Thus, an entirewavelength is a rather large granularity for resource allocation in anoptical communication system. A need therefore exists for a moreefficient mechanism for switching optical signals at the wavelengthlevel, especially at the core of an optical network. A further needexists for a scalable approach for implementing systems comprised oflarge number of optical flows, and a heterogeneous mix of everincreasing information rates upon each such flow.

SUMMARY OF THE INVENTION

[0008] Generally, an optical packet tray router is disclosed thatmanipulates signal wavelength as the fundamental control mechanism. Thedisclosed optical packet tray router aggregates one or more packets in apacket tray for transmission over a network. The packet trays provide amechanism for switching at the wavelength level. The packet trays carryone or more packets through an optical communication system andrepresent the routable entity with a finer grain size than wavelengthcircuit switched systems, since each packet tray can be dynamically, intime and space, assigned a unique wavelength.

[0009] An exemplary N×N optical packet tray router employs wavelengthdivision multiplexing techniques to transmit m information signals(i.e., packet trays) on the same physical channel. The optical trayrouter includes a control section and a data section. According to oneaspect of the invention, the data section processes only opticalsignals. The disclosed optical tray router switches a packet trayreceived on one of N input channels to one of N appropriate outputchannels, with an appropriate wavelength, based on associated headerinformation and routing protocol algorithm. The payload portion of allthe packet trays in a given time slot are processed in parallel asoptical signals. The header information associated with each packettray, together with a routing algorithm and local system stateinformation, are used to route each packet to the appropriatedestination channel and to make timing decisions. The packet traypreamble is used to establish a timing reference for the physical inputchannel with respect to the local time reference associated with theoptical packet tray router. In this manner, all wavelength divisionmultiplexed packet tray streams are associated with a timing offsetrelative to the local optical packet tray router timing reference. Thetiming offsets are used to align the (wavelength and spatiallydemultiplexed) packet tray streams.

[0010] A disclosed wavelength server (also referred to as a lambdaserver) generates optical control wavelengths in response to the timingdecisions. The wavelength server efficiently and dynamically generatesthe unique required continuous wave (CW) light, of an appropriatewavelength, that is used to direct control points within the opticaldata path. In the optical packet tray router, these continuous wavelight sources establish the fundamental mechanism for controllingelements within the optical packet tray router. By realization of thewavelength server in a centralized and scalable disclosed method,distribution of numerous and complex electrical control signals areavoided in the OPTR.

[0011] A generated optical control wavelength is used to adjust thewavelength of a given packet tray and thereby introduce a wavelengthselective delay to the packet tray. Wavelength selective delays can beemployed to align packet trays or to shift one or more packet trays toavoid a collision within the switch fabric. According to one aspect ofthe invention, each packet tray in a given time slot is time aligned toa master clock start of packet tray reference using a tunable opticaldelay. The tunable optical delay allows a given packet tray to beshifted in time using a coarse or a fine time adjustment (or both). Awavelength selective coarse delay adjustment is achieved using amulti-wavelength Bragg grating that shifts a packet tray based on theoptical control wavelength assigned to the packet tray. A wavelengthselective fine delay adjustment is achieved using a dispersive mediumwhere the transmission time through the dispersive medium is a functionof the optical control wavelength assigned to the packet tray. Eachdistinct optical control wavelength introduces a different delay throughthe coarse and fine delay elements.

[0012] According to one aspect of the invention, a k-deep random accesswrite buffer introduces a wavelength selective delay that ensures thattwo packet trays are not going to the same output channel at the sametime, using the known destination information thus avoiding a packettray collision. The k-deep random access write buffer will timetemporally shift a packet tray by up to k time slots, where each timeslot has a duration approximately equal to a packet tray interval. Theexemplary k-deep random access write buffer includes k coarse delayelements, such as multi-wavelength Bragg gratings, each separated by acorresponding fixed delay element.

[0013] Once a header processor identifies a delay to be assigned to agiven packet tray at a given stage in the packet tray router, thewavelength of the packet tray is converted to the control wavelengthcorresponding to the identified delay, irrespective of the initialwavelength of the packet tray or the initial channel upon which thepacket tray was received at the packet tray router. At the output stageof the packet tray router, the packet tray wavelength can be convertedto any desired output channel wavelength.

[0014] The disclosed optical packet tray router architecture may beviewed as a pipelined, staged architecture. Each stage is implemented intwo steps. In a first step, each stage in the switch architecturetypically receives two inputs. One input is from the prior switch stageoutput, and the other input is the continuous wave wavelength providedby the wavelength server as appropriate. The two inputs are combined toprovide signal restoration, (e.g., amplification, shaping and possiblyretiming) as well as wavelength conversion, all in the optical domain.In a second step, the restored and recolored signal is then presented tothe passive optical elements that implement the desired function forthat architecture stage. The overall switch architecture is instantiatedby a cascade of such stages. The wavelength grid internal to the switchis engineered separately from the external optical interfaces. Theexternal interface wavelengths typically need to conform to an industrystandard defined WDM grid structure, such as the wavelength gridstructure established by the ITU.

[0015] A more complete understanding of the present invention, as wellas further features and advantages of the present invention, will beobtained by reference to the following detailed description anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 illustrates a packet tray incorporating features of thepresent invention;

[0017]FIG. 2 is a schematic block diagram of an N×N optical tray routerin accordance with the present invention;

[0018]FIG. 3 illustrates a schematic block diagram of a signal levelrestoration/regeneration element incorporating features of the presentinvention;

[0019]FIG. 4 is a schematic block diagram of an optical routerillustrating a fixed delay that is introduced to mask the time requiredto process the tray header;

[0020]FIG. 5 is a schematic block diagram illustrating a delay schemeused by the alignment stage of FIG. 2 to align each of the N×m packettrays;

[0021]FIG. 6 is a schematic block diagram illustrating a particularimplementation of the delay scheme of FIG. 5;

[0022]FIG. 7 is a schematic block diagram illustrating a k-deep randomaccess write buffer used by the rescheduler of FIG. 2;

[0023]FIG. 8 is a schematic block diagram illustrating an alternatek-deep random access write buffer used by the rescheduler of FIG. 2;

[0024]FIGS. 9A through 9G illustrate various implementations usingSilicon optical bench (SiOB) techniques to implement the fixed delayelements of FIGS. 7 and 8;

[0025]FIG. 10 illustrates a technique for dropping the previous headerinformation and inserting new header information for the next switch ornode;

[0026]FIG. 11 is a schematic block diagram of one embodiment usingtraditional optical bench techniques for a wavelength server of FIG. 2;

[0027]FIG. 12 is a schematic block diagram of an alternate embodimentusing integrated electro-optics and silicon optical bench techniques fora wavelength server of FIG. 2; and

[0028]FIG. 13 is a schematic block diagram illustrating anotheralternate “p-way concurrent”, k-deep random access write buffer used bythe rescheduler of FIG. 2.

DETAILED DESCRIPTION

[0029] The present invention provides an optical communication systemthat aggregates one or more packets in a packet tray 100, withconstituent parts shown in FIG. 1, for transmission over a network. Thepresent invention recognizes that wavelengths are finite in number andexpensive to provision. Thus, an entire wavelength is a rather largegranularity for resource allocation in an optical communication system.The packet trays 100 of the present invention provide a mechanism forswitching at the wavelength level. The packet trays 100 carry one ormore packets through an optical communication system and represent theroutable entity with a finer grain size, since each tray can be assigneda unique wavelength.

[0030] A router or switch in accordance with the present invention, suchas the optical tray router (OPTR) 200, discussed below in conjunctionwith FIG. 2, provides space and wavelength selection in order to routeeach packet tray 100 to the appropriate destination. The disclosedoptical tray router 200 provides space selection by switching a packettray 100 received on one of N input channels to an appropriate outputchannel based on the associated header information. The optical trayrouter 200 provides wavelength selection using wavelength divisionmultiplexing techniques to transmit m information signals (packet trays100) on the same channel.

[0031] According to one aspect of the invention, a router or switch inaccordance with the present invention, such as the optical tray router200 of FIG. 2, provides an optical data path, such that only opticalsignals are processed, and conversion between optical and electricalsignals is not required. In order to maintain an optical signal ofsufficient intensity at each stage of an optical communication system,the present invention provides a system for restoring the opticalsignals using a wavelength server 285, discussed below in conjunctionwith FIGS. 2, 11 and 12. As discussed further below, the wavelengthserver 285 generates lights of desired wavelengths in order to restorethe optical signals.

[0032] According to another aspect of the invention, a number oftechniques are disclosed for introducing a wavelength selective delay.For example, each of the packet trays in a given time slot are timealigned using a tunable optical delay. The tunable optical delay allowsa given packet tray to be shifted in time using a coarse or a fine timeadjustment (or both). In addition, wavelength selective delays areemployed by the present invention to ensure that two packet trays arenot going to the same output channel at the same time, using the knowndestination information.

[0033]FIG. 1 illustrates an exemplary packet tray 100 in accordance withthe present invention. As shown in FIG. 1, a packet tray 100 istypically of a fixed length 110, comprised of a tray header 120 and apayload 130. In operation, the optical tray router 200 incorporates thefollowing features. Each physical input channel is wavelengthdemultiplexed to separate the streams of packet trays. The packet traypreamble is used to establish a timing reference for the physical inputchannel with respect to the local time reference associated with theoptical tray router 200. (The local time reference may or may not beslaved to a global network time.) This timing reference is tracked tomaintain the “beginning of packet tray” time reference for a givenphysical channel. Resynchronization of the physical channel will berequired if the source network node or an intervening cross-connectre-establishes the physical connection. It is during this procedure thatthe packet tray header clock rate synchronization and lock isestablished through burst mode timing recovery methods. The headerinformation 120 is extracted from each packet tray 100. The header andpayload clocks and clock rates need not be the same. In this manner, allwavelength division multiplexed-packet tray streams associated each andevery input physical channel are associated with a timing offsetrelative to the local optical tray router timing reference. The timingoffsets are used to align the (wavelength and spatially demultiplexed)packet tray streams. In general, all packet trays need not be ofidentical maximum length. However, it is assumed that the maximum lengthis chosen to insure efficient utilization of trays and effective serviceto the payload packets. Hence, the scheduling epoch and granularity isthat associated with the packet tray itself. Alignment of the traysenables the establishment of a time slotted switch element resourceallocation method.

[0034] Since only the packet tray header information is interpreted bythe optical tray router 200, the form and rate of the payloadinformation (e.g., the “packets”) is unconstrained and effectivelytransparent to the optical tray router 200. This provides a highlyscalable routing and switching architecture adapting transparently todiverse payload data rates and formats. The header information rate maybe established to establish ease of processing implementation whileensuring efficient use of network resources. In general, the headerduration should be short with respect to the packet tray payloadinterval. In addition, time alignment for the header portion of thepacket tray format and the payload portion of the packet tray formatwill be established within some uncertainty interval. This interval isincorporated into the OPTR packet format and may be engineered tominimize the impact on overall system performance. The headerinformation 120 is processed using a routing algorithm together with arepresentation of the local switch resource state to yield control andtiming decisions that direct the overall switch architecture operation.The establishment of timing offset, header decoding and headerprocessing may be performed in an all optical manner, an all electronicmanner or using a hybrid approach.

[0035] The tray header 120 shown in FIG. 1 is typically of a fixedlength and includes the source/destination or virtual packet trayidentifier that will be used together with routing information andoptical tray router internal state information within the headerprocessing 280 (FIG. 2) to determine the appropriate paths and delaysthrough the switch for steering the packet tray 100. The payload 130 iscomprised of one or more packets that may optionally be of variablesize. In addition, the exemplary packet tray 100 includes tray delimitflags 140, 150 indicating the start and end of a packet tray 100,respectively.

[0036] Generally, the tray header 120 should be small relative to thesize of the payload 130. In order to maintain a tray transportefficiency of 95%, for example a packet tray could be characterized by apayload transmission rate of 10 GHz, a tray header 120 duration of 100nS and a payload 130 should contain 2.5 Kilobytes. The parameters shownyield viable implementation and performance characteristics such asthroughput efficiency and reasonable latencies. Implementationconsiderations include viability of implementing delay structures,control processing intervals, and control set up times. Many otherparameter sets yield acceptable implementations. The following tablespecifies a number of parameters for the optical tray router 200 for anumber of efficiency levels: Structural/ payload Efficiency size 98%bytes 250 kB 25 kB 62.5 KB 6.25 KB Data Clock bps 4.00E+10 4.00E+101.00E+10 1.00E+10 Rate packet tray seconds 5.22E−05 5.22E−06 5.22E−055.22E−06 duration header equiv bits 40000 4000 10000 1000 bits w/framing header time seconds 1.00E−06 1.00E−07 1.00E−06 1.00E−07 packetpay- seconds 5.12E−05 5.12E−06 5.12E−05 5.12E−06 load time efficiency =percentage 98% 98% 98% 98% Payload/ Tot Duration Structural payloadEfficiency size 95% bytes 100 kB 10 kB   25 kB  2.5 kB Data Clock bps4.00E+10 4.00E+10 1.00E +10 1.00E+10 Rate packet tray seconds 2.15E−052.15E−06 2.15E−05 2.15E−06 duration header equiv bits 40000 4000 100001000 bits w/ framing header time seconds 1.00E−06 1.00E−07 1.00E−061.00E−07 packet pay- seconds 2.05E−05 2.05E−06 2.05E−05 2.05E−06 loadtime efficiency = percentage 95% 95% 95% 95% Payload/ TotDurationStructural payload Efficiency size 91% bytes  50 kB  5 kB 12.5 kB 1.25kB Data Clock bps 4.00E+10 4.00E+10 1.00E+10 1.00E+10 Rate packet trayseconds 1.12E−05 1.12E−06 1.12E−05 1.12E−06 duration header equiv bits40000 4000 10000 1000 bits w/ framing header time seconds 1.00E−061.00E−07 1.00E−06 1.00E−07 packet pay- seconds 1.02E−05 1.02E−061.02E−05 1.02E−06 load time efficiency = percentage 91% 91% 91% 91%Payload/ TotDuration

[0037]FIG. 2 is a schematic block diagram of an N×N optical tray router200 in accordance with the present invention. The optical tray router200 employs wavelength division multiplexing techniques to transmit minformation signals (packet trays 100) on the same channel. As shown inFIG. 2, the optical tray router 200 includes a control section 210 and adata section 220. The data section 220 processes only optical signals inaccordance with the present invention, and the control section 210 mayprocess optical signals or electrical signals (or both). The disclosedoptical tray router 200 switches a packet tray 100 received on one of Ninput channels 215-1 through 215-N to one of N appropriate outputchannels 268-1 through 268-N based on the associated header information120.

[0038] As shown in FIG. 2, the optical tray router 200 includes N inputchannels 215-1 through 215-N, each having an associated opticalamplifier 225-1 through 225-N. Thereafter, each of the N input channelsare demultiplexed to separate the m packet trays 100 using acorresponding optical demumultiplexer 230-1 through 230-N. Thereafter,the N×m packet trays 100 are processed in parallel as optical signals inthe optical tray router 200. There is an optical splitter 235-i-j and analignment stage 240-i-j associated with each of the N×m packet trays100.

[0039] The optical splitters 235-i-j allocate a portion of the opticalenergy for processing by the control section 210. The control section210 recovers the clock and monitors the incoming data until a traydelimit flag 140 is detected indicating the start of a new packet tray100. It is noted that while the header information is distinct for eachsplitter 235-i-j, it is possible, depending on the overall networkarchitecture that all m demultiplex outputs from a physical opticalchannel share common timing information. This attribute may be exploitedto reduce complexity in clock recovery and preamble detect processing.Thereafter, the header information 120 is analyzed with respect tostored network routing information to determine the appropriate outputchannel 268 to route the packet tray to the header indicated destinationor virtual packet tray identifier if cut through routing techniques areutilized. As discussed below in conjunction with FIG. 4, a fixedarchitectural delay is introduced subsequent to each splitter 235 tomask the delay caused by the header processing and to keep theappropriate header information aligned with the corresponding data. Itis noted that after the splitters 235 copy the packet tray headerinformation for use by the control processing section 210, the headerportion 120 of the packet tray 100 may be reused for other purposes. Onesuch purpose is to provide a required control setup interval for eachswitching stage.

[0040] The optical splitters 235-i-j allocate most of the optical energyfor processing by the data section 220. As shown in FIG. 2 and discussedfurther below in conjunction with FIGS. 5 and 6, the data section 220includes an alignment stage 240-i-j associated with each of the N×mpacket trays 100. Generally, each alignment stage 240-i-j aligns thestart of the corresponding packet tray 100, using tray delimiterinformation from the control section 210 and tunable optical delays inaccordance with the present invention.

[0041] The aligned packet trays 100 are then processed by a re-scheduler250, discussed below in conjunction with FIGS. 7 and 8. The re-scheduler250 ensures that two packet trays 100 are not going to the same outputchannel at the same time, using routing information received from thecontrol section 210. Generally, in the event that two packet trays 100are going to the same output channel at the same time, the re-scheduler250 delays at least one packet tray until another time interval. Thedepth of available packet delays are chosen to limit the probability ofa dropped packet to an arbitrary OPTR architecture design value basedupon the ingress traffic characteristics.

[0042] The N×m optical packet trays 100 are restored, wavelengthconverted, and amplified by an associated optical device 255-1-1 through255-N-m and then switched to the appropriate output channel by aswitching stage 260, based on control information received from thecontrol section 210. Example optical devices used for signalrestoration, retiming, gain and wavelength conversion include: MachZehnder interferometers with semiconductor optical amplifiers (SOAs),delay interferometers with SOAs and non-linear optical waveguidetechniques based upon multiple wave mixing. The switching stage 260 maybe embodied, for example, using the switch fabric scaling techniquesdescribed in, e.g., Charles Clos “A Study of Non-Blocking SwitchingNetworks,” Bell System Technical Journal, Vol. XXXII, 406-24, (March,1953); or Chuan-Lin Wu and Tse-Yun Feng, “Tutorial: InterconnectionNetworks for Parallel Processing,” IEEE Computer Society ISBN0-8186-0573-X, 127-44, (1994), each incorporated by reference herein.The optical equivalent of the switching element building block of theseinterconnected structures, in keeping with the OPTR architecturalprinciples, includes an active wavelength conversion stage with theappropriate optical control signals from the Lambda Server, followed bya passive optical WGR. These switch building blocks are theninterconnected in analogous manners to multi-stage interconnectionschemes, such as the Clos topology referenced above.

[0043] Implicit in the output WDM stage in FIG. 2, 265-1 through 265-Nis a restoration/regeneration/wavelength conversion stage to ensureproper processing in the subsequent wavelength multiplexing operation.FIG. 3 depicts this signal conditioning function. In addition, thisstage represents the last opportunity to “re-write” the headerinformation required to create a well-formed packet tray usingtechniques depicted in FIG. 10. The header processing creates the newoutbound header and provides it in an optical form to the signalconditioning function associated with the output multiplexers 265. Itmay be merged into the outbound stream at the appropriate wavelength.Note that this header re-write function may also be accomplished inearlier stages of the optical tray router 200, depending uponimplementation trades.

[0044] The m optical packet trays 100 associated with each of the Noutput channels are then multiplexed onto the corresponding fiber usingoptical multiplexers 265-1 through 265-N. The optical multiplexers 265,as well as the optical demultiplexers 230, may be embodied, for example,as waveguide grating routers (WGR), such as the optical star couplersdescribed in U.S. Pat. No. 4,904,042 to Dragone, incorporated byreference herein.

[0045]FIG. 3 illustrates a schematic block diagram of a signal levelrestoration/regeneration/wavelength conversion element 300,incorporating features of the present invention. As shown in FIG. 3, thesignal level restoration/regeneration/wavelength conversion element 300initially restores an input optical signal at stage 310 by convertingthe wavelength to the appropriate wavelength for the current packet tray100 and regenerating the signal level and waveform (and removing anydispersion), using a tunable continuous wave light received from thewavelength server 285, discussed further below. Thereafter, photonicprocessing is performed on the optical signal at stage 320, such asswitching, alignment, multiplexing or delay. Following the photonicprocessing, the optical signal is again restored at stage 330 byconverting the wavelength to the appropriate wavelength for the currentpacket tray 100 and regenerating the signal level, using a tunablecontinuous wave light received from the wavelength server 285. Theserestoration/regeneration/wavelength conversion stages may be placed asnecessary in the multi stage optical tray router architecture tomaintain signal fidelity and ensure wavelength conversion for subsequentstage processing. All required such stages are not explicitly shown inFIG. 2. In addition, the header re-write function may also beincorporated, as discussed further below in conjunction with FIG. 10, inthis stage.

[0046] The wavelength conversion and signal restoration at stages 310and 330 may be performed, for example, by Mach Zehnder interferometers,such as those described in Katsunari Okamoto, “Fundamentals of OpticalWaveguides,” 159, Academic Press (2000), incorporated by referenceherein. As previously indicated, the optical tray routers 200 of thepresent invention have N input channels, each containing m WDMmultiplexed wavelength channels. If there are p required restorationstages, then the number of required restoration elements 300 grows asN×m×p.

[0047] Header Processing Delay

[0048]FIG. 4 is a schematic block diagram of an optical router 400illustrating a fixed delay 410 that is introduced to mask the timerequired to process the tray header 120. The header processing section420 of FIG. 4 corresponds to the control section 210 of FIG. 2 and theoptical section 430 of FIG. 4 corresponds to the data section 220 ofFIG. 2. Thus, the optical tray router 200 of FIG. 2 would introduce adelay after the splitter stage 235 in order to keep the data alignedwith the corresponding header information. The header interval in eachpacket tray 100 provides a setup time for optical elements. Thisinterval should be as small as possible to minimize the packet traysize, and hence the delay line length in the random access bufferportion of the architecture (although the header interval must be largeenough to carry label information used for routing such assource/destination addresses or virtual packet tray identifiers for cutthrough routing techniques).

[0049] The delay introduced by the delay 410 provides a latency impacton system performance. While the delay affects the length of the frontend delay line, it is unrelated to tray sizing with respect toefficiency. Minimizing this duration helps to simplify the delay lineimplementation.

[0050] Optical Alignment Delays

[0051]FIG. 5 is a schematic block diagram illustrating a delay scheme500 used by the alignment stage 240 to align each of the N×m packettrays 100 in the optical tray router 200. As shown in FIG. 5, eachpacket tray 100 can be aligned using a variable coarse delay 510 or avariable fine delay 520 (or both). This particular arrangement enablesthe realization of delays over a wide range of delay values.

[0052]FIG. 6 is a schematic block diagram illustrating a particularimplementation of the delay scheme 500 of FIG. 5. As shown in FIG. 6, apacket tray 100 of a given wavelength has its wavelength converted andrestored by a wavelength converter/restorer 610 to a new wavelength,λ_(desired coarse delay), having a corresponding coarse delay amount.The packet tray 100 then passes through an optical circulator 620 into amulti-wavelength Bragg grating 630. For a more detailed discussion ofBragg gratings, see, for example, Raman Kashyap, Fiber Bragg Gratings,Academic Press, Section 6.5, Optical Circulator Based OADM, 265-70 (ISBN0-12-400560-8), incorporated by reference herein. Using the coarse/fineapproach, this arrangement enables implementation of delays over a widerange of delay values while reducing the performance requirements oneach constituent component of the scheme.

[0053] Generally, a Bragg grating is a fiber or wave guide etched withlines such that light of a given wavelength will be reflected in acertain region of the waveguide. For example, if light of a wavelength,λ_(k), enters the Bragg grating, the light will be reflected in thethird region identified in the example of FIG. 6. Each wavelength regionin the Bragg grating will introduce a corresponding delay based upon thelength of integrated waveguide or fiber between gratings and upon theround trip time of the light. For example, the exemplary Bragg grating630 may permit a coarse delay of, e.g., 5, 10, 15 or 0.20 μsec to beselectively introduced for wavelengths, λ_(i), λ_(j), λ_(k), or λ_(l),respectively. Thus, the wavelength converter 610 is configured to adjustthe wavelength of a packet tray 100 to a new wavelength,λ_(desired coarse delay), selected from the group of wavelengths, λ_(i),λ_(j), λ_(k), or λ_(l).

[0054] Following reflection in the Bragg grating 630, the packet tray100 having a wavelength, λ_(desired coarse delay), will pass through theoutput port of the optical circulator 620 to a second wavelengthconverter/restorer 640 that converts the wavelength of the packet tray100 to a new wavelength, λ_(desired fine delay), having a correspondingfine delay amount. The fine delay amount may be, e.g., on the order of0-5 micro-seconds.

[0055] The packet tray 100, now having a wavelength,λ_(desired fine delay), is then applied to a dispersive medium 650,where the transmission time through the media 650 is a function ofwavelength. In this manner, the wavelength, λ_(desired fine delay), ofthe packet tray 100 can be selected to introduce a desired vernierdelay, as described in J. P. Lang et al., “The λ-Scheduler: AMultiwavelength Scheduling Switch,” J. on Lightwave Technology, Vol, 18,No. 8, (August 2000), incorporated by reference herein. The delayedpacket tray 100, having a wavelength, λ_(desired fine delay), is thenapplied to a third wavelength converter 660 that converts the wavelengthof the packet tray 100 to a new wavelength, λ_(desired next stage),having a wavelength that is appropriate for the next stage. In theoptical tray router 200, the next stage after the alignment stage 240 isthe re-scheduler 250, discussed below in conjunction with FIGS. 7 and 8.

[0056] The following paragraph discusses the control of desired coarseand fine delay wavelength generation. For each packet tray 100, thecontrol path 210, using clock recovery and preamble detect information,analyzes the extent to which the tray 100 deviates from a OPTR masterclock start of packet tray reference and determines the appropriatedelay amount. The wavelength server 285 is commanded to deliver, by thecontrol path 210, the appropriate light sources λ_(desired coarse delay)and λ_(desired fine delay) to the alignment stage 240-i-j that isprocessing the corresponding packet trays 100. If the physical network(fiber) configuration and the predecessor OPTR node is operating undernominal conditions, once the initial alignment is set, furtheradjustments to the packet tray alignment are of an incremental, ortracking, nature. However, architectural support of rapid re-alignmentimproves OPTR robustness in the face of rapid and often networkreconfigurations.

[0057] The wavelength converters/restorers 610, 640, 660 may be embodiedusing the same technology as discussed above in conjunction with FIG. 3to restore an input optical signal by converting the wavelength to theappropriate wavelength and regenerating the signal level (and removingany dispersion). For example, the wavelength converters/restorers 610,640, 660 may be embodied as Mach Zehnder interferometers usingsemiconductor optical amplifiers with interferometers (SOA-I), delayloop interferometers, non-linear optical pumping effects, or any otherequivalent mechanism.

[0058] Packet Tray Re-Scheduler

[0059] As previously indicated, the aligned packet trays 100 areprocessed by a re-scheduler 250 to ensure that two packet trays 100 arenot going to the same output channel at the same time, using routinginformation received from the control section 210. Generally, in theevent that two packet trays 100 are going to the same output channel atthe same time, the re-scheduler 250 delays at least one packet trayuntil another time interval. (As discussed previously, the depth of therescheduling buffer may be engineered for a particular probability of“packet-drop” for given traffic models.) The re-scheduler 250 may beembodied as a k-deep random access write buffer 700, shown in FIG. 7,incorporating features of the present invention. Generally, the k-deeprandom access write buffer 700 will time shift (delay) a packet tray 100by up to k time slots, where each time slot has a duration equal to apacket tray interval. As shown in FIG. 7, the exemplary k-deep randomaccess write buffer 700 includes k coarse delay elements 720-i through720-k, such as multi-wavelength Bragg gratings 630 (FIG. 6), eachseparated by a corresponding fixed delay element 730-i through 730-k.The fixed delay elements 730 may be embodied, for example, as a woundfiber loop or an integrated waveguide leveraging Silicon optical bench(SiOB) techniques. (It is also noted that these delay elements providean opportunity for incorporating optical gain through waveguide/fiberdoping and optical pumping, if needed, for signal level equalizationwithin the delay elements themselves.)

[0060] The total delay through a coarse delay element 720 and acorresponding fixed delay associated with the Bragg element 730 shouldbe equal to a packet tray interval. The delay through the coarse delayelement 720 will be small.) Thus, if a packet tray is reflected in thefirst stage, 720-i, then essentially no delay is introduced to thepacket tray 100 (and the tray 100 is not time shifted). The stage thatreflects a given packet tray is determined by the wavelength,λ_(desired buffer delay), of the packet tray following conversion by theconverter/restorer 710, in the manner described above in conjunctionwith FIG. 6.

[0061] If the control processing path 210 determines that a given packettray 100 needs to be shifted by one or more time intervals to avoid acollision, the wavelength server 285 delivers the appropriate lightsource, λ_(desired buffer delay), for the packet tray 100 to there-scheduler 250. If a packet tray is reflected in the second stage,720-j, for example, then a delay of one packet tray interval isintroduced to the packet tray 100. Generally, if a packet tray isreflected in the k-th stage, 720-k, then a delay of k packet trayintervals is introduced to the packet tray 100.

[0062] Once reflected, the packet tray 100 is summed at stage 760 withall other packet trays, which relies on the fact that only one tray willbe present at a given time (thus, implying N×m summers). Thus, each ofthe N×m packet trays can be selectively time shifted by up to k timeslots, using an array of the k-deep random access write buffers 700.Thereafter, the wavelength of the packet tray 100 is converted atconversion stage 770 to a new wavelength, λ_(desired next stage), havinga wavelength that is appropriate for the next stage. In the optical trayrouter 200, the next stage after the re-scheduler 250 is the switchingstage 260. The preparatory signal restoration/gain/wavelength conversionis shown on the system architecture diagram, FIG. 2, 255. This functionis equivalent to the blocks shown in FIG. 7, items 770 and 780. Thedesired wavelength is a function of the next stage operation and isdescribed in the Switching 260 section.

[0063]FIG. 8 illustrates an alternate implementation of the k-deeprandom access write buffers 700 of FIG. 7, where the N×m summers 760have been replaced by a fewer number of waveguide grating routers (WGR)860. The chain of k coarse delay elements 820 and corresponding fixeddelay elements 830 may be embodied in the same manner as described abovein conjunction with FIG. 7. Rather than having N×m summers 760, however,the alternate k-deep random access write buffer 800 includes a smallernumber of waveguide grating router (WGR) 860. The WGR 860 receives ksignals for each of the n input channels. Only one of the k signals foreach of the n number of WGR input channels will be active in a giventime slot. The WGR 860 integrates the k signals for each of the n inputchannels and provides a corresponding output for each of the n number ofWGR output channels utilized. The maximum port size of the WGR dictatesthe reduction in summer complexity achieved. Hence, if the number ofchannels that could be processed by a single WGR, is “W”, then thenumber of WGRs required scales as (N×m)/W. The number of channels thatmay be processed by each WGR with a given port dimension is a functionof buffer depth “k”.

[0064] Thus, each of the N×m packet trays can be selectively timeshifted by up to k time slots. Thereafter, the wavelength of each packettray 100 is restored, amplified and converted at conversion stage 870-iand 880-i to a new wavelength, λ_(desired next stage), having awavelength that is appropriate for the next (switching) stage.

[0065]FIGS. 9A through 9G illustrate various implementations usingSilicon optical bench (SiOB) techniques of the fixed delay elements 730,830 of FIGS. 7 and 8. The techniques shown in FIGS. 9A through 9G permitdelays on the order of tens of microseconds to be achieved. Generally,the overlapping orthogonal geometries shown in FIGS. 9A through 9G allowseveral delay lines to be incorporated on a single wafer. FIGS. 9Athrough 9E illustrates various orthogonal spiral packing on a singlewafer. Generally, each configuration provides intersection points thatare orthogonal to one another. FIG. 9F illustrates two bounding radii ofa spiral delay line, where a smaller radius than the minimum radius isnot allowed due to the minimum “bend.” FIG. 9G illustrates an exemplarytechnique for achieving ingress and egress of the optical signals. It isnoted that doping materials can be utilized to enhance the index ofrefraction distances between the waveguide core and the boundarymaterial, thereby reducing the minimum bend geometries that may beestablished. Additionally, alternative entry/exit methods may beemployed using integrated “mirror” structures within the waveguidecombined with multiple waveguide layers or novel packaging concepts.Integration of several delay structures within a small area supports thescaling attributes of the OPTR architecture described herein by reducingthe number of distinct elements needed for implementation.

[0066] At each routing or switching node within an optical communicationsystem, the header information 110 of a packet tray 100 must be updatedto include the routing information for the next node. FIG. 10illustrates a technique for dropping the previous header information 110and inserting new header information for the next node. As shown in FIG.10, a WDM demultiplexer 1010 separates the optical signal into eachrespective channel. An optical splitter 1015 then divides the opticalsignal so that the data and control sections can be separatelyprocessed. The header information is analyzed at stage 1025 to performtiming recovery, header bit synchronization and header or framedetection. The detected header information 110, together with a routingalgorithm and topology information (or analogous information used forcut-through routing techniques), is used to properly configure therouter 200, e.g., in order to switch each packet tray 100 to theappropriate output channel, and then to update the header informationfor the next stage. Each output channel of the router 1000 uses aninterferometer device 1030, such as a SOA/I device, to delete the priorinformation bits 1037 and insert the appropriate header bits 1039 tocreate the well formed packet tray header 1041 for the next switching orrouting node. Finally, the packet trays from each of the channels arethen combined in the final wavelength multiplexing stage 1040. Thistechnique is applied within the OPTR architecture described above.

[0067] Wavelength Server

[0068]FIG. 11 is a schematic block diagram of one embodiment of awavelength server 1100 incorporating features of the present invention.As shown in FIG. 11, a wavelength server 1100 includes a broadband lasersource 1110 covering the wavelengths of interest. The generated light isapplied to an optical gain stage 1120 in order to increase the powerbefore it is split many times. The amplified light source is thenapplied to a free space optical system including lenses 1125 and 1130that spread the wave front spatially and create a parallel wave frontthat is incident upon a tunable grating array 1135. The tunable gratingarray 1135 is an electrical grating array control element that provideswavelength selection for each array element. Generally, each element ofthe tunable grating array 1135 can select light of a desired wavelength.(This may be accomplished by tuning the resonant wavelength of thefilter cavity through electrical, or other means.)—A set of micro balllenses 1140 may be used to couple the tunable grating array 1135 to afiber bundle array 1150 which in turn couples the lights toappropriately lensed ribbon fibers 1155. Direct coupling or expandedbeam coupling, as described, may be used.

[0069]FIG. 12 is a schematic block diagram of another embodiment of awavelength server 1200 incorporating features of the present invention.The wavelength server 1200 includes a broadband laser source 1210,optical gain stage 1220, and fiber bundle array 1250 that couples thelights to ribbon fibers 1255 that operate in the same manner as thecorresponding elements of FIG. 11, discussed above. While the wavelengthserver 1100 of FIG. 11 employed free space optical signals, thewavelength server 1200 of FIG. 12 employs optical components in anintegrated SiOB device. The silicon optical bench based lens 1225,tunable grating array 1235 and micro ball lenses 1240 operatefunctionally in the same manner as discussed above in conjunction withFIG. 11.

[0070] p-Way Concurrent k-Deep Random Access Write Buffer

[0071]FIG. 13 illustrates an alternate implementation 1300 of the k-deeprandom access write buffer of FIGS. 7 and 8 that multiplexes pwavelengths concurrently and contemporaneously onto the same structure.While the k-deep random access write buffers of FIGS. 7 and 8 delayedone packet tray by a desired amount, the k-deep random access writebuffer 1300 of FIG. 13 delays p signals by a desired amount for eachtime interval. Each of the k coarse delay elements 1320 contains presonances to handle up to p groups of wavelengths simultaneously. Inother words, each coarse delay element 1320 reflects up to p distinctwavelengths. The corresponding fixed delay elements 1330 may be embodiedin the same manner as described above in conjunction with FIG. 7.

[0072] The wavelength of a given packet tray is converted by aconverter/restorer 1310 to multiplex the packet tray with up to p-Iadditional packet trays. By appropriate selection of the desired bufferdelay wavelengths in the converter/restorer stage 1310, each of themultiplexed packet trays can be delayed by any one of the k possiblebuffer delay amounts. If a given packet tray is reflected in the firststage, 1320-i, then essentially no delay is introduced to the packettray 100 (and the tray 100 is not time shifted). The stage that reflectsa given packet tray is determined by the wavelength,λ_(desired buffer delay), of the packet tray following conversion by theconverter/restorer 1310, in the manner described above in conjunctionwith FIGS. 6 and 7. The “p-way concurrent,” k-deep random access writebuffer 1300 can thus process up to p groups of k wavelength signalssimultaneously, within a single cascade of “circulator-bragggrating—delay” structures shown in FIG. 13.

[0073] As an example of the parameters involved, assume that k, thedepth of the re-ordering buffer is four, and the dimension of the WGR is256×256 ports. Then, each input signal will require four wavelengths toaccomplish the desired delay. For this signal, four of the WGR inputports will be required—corresponding to the four possible signal delays.Groups of four input channels to the WGR service a subset of the N×minput packet tray streams. Each of sixty four WGR outputs will containthe appropriately delayed and reordered packet trays. In thisintroductory example, each Bragg grating is used to reflect a singlewavelength, after an appropriate delay, to the WGR-based combiningfunction. Now assume that each grating will reflect p wavelengthmultiplexed signals, while allowing the others to pass through. Byorganizing the wavelength mapping performed by the input signalrestoration and wavelength conversion functional block to support boththe appropriate reordering delay of a given input signal and thereordering delay function across multiple input signals (p), p-wiseconcurrent operation is achieved. Given that 256 distinct wavelengthsmay be applied by the up-front wavelength conversion function, 64 inputchannel groupings, each group of size four wavelengths may be defined.

[0074] Wavelengths are distinct and ordered, e.g. sequentially. In thismanner, wavelength collisions are avoided within the reordering bufferstructure. The first input channel is colored according to the firstgroup of four wavelengths, the second input channel is colored accordingto the second group of four wavelengths, and so forth. If p is taken tobe 64, sixty four signals, wavelength converted (or colored) to one of256 wavelengths are present in the “circulator-Bragg grating-delay”structure after coupling. Similarly, only four WGR inputs, e.g. thedepth of the re-ordering buffer, need be used since these four inputsrepresent 256 possible colorings. Hence, 64 “circulator-Bragggrating-delay” structures, 256 connections from the appropriate delaysto the WGR input ports, and a total of 256 WGR input ports are used whenorganized in accordance with FIG. 8. The arrangement depicted in FIG. 13requires a single “circulator-Bragg grating-delay” structure, and fourinterconnections from the appropriate delays to the WGR input ports, anda total of four WGR input ports. For p equal to 64, a 64-way coupler atthe front-end is required to combine the wavelength converted, 64 inputsignals for presentation to the “circulator-Bragg grating-delay”structure.

[0075] Hybrids between FIG. 8 and FIG. 13 are allowed. Implementationdetails dictate ease of physical instantiation or cost or performance ofa given implementation. Through appropriate wavelength selection, fullutilization of the WGR ports is achievable. The improved utilization isdue to the ability to more fully utilize each WGR input port, allowing amultiplicity (p) of wavelength multiplexed signals on each input port.The input channels for the buffer may be freely chosen from the, alreadyaligned, N×m input channels from the OPTR.

[0076] It is noted that the structure in FIGS. 7, 8 and 13 define afull, all optical switch fabric, as well as reordering buffers, in theirown right. The output packet trays may be shifted in time, space andwavelength. The OPTR architecture allows scalability through areplication of these optical switches, and their subsequent injectioninto a fully scalable switch fabric 260.

[0077] The k-deep random access write buffer 1300 includes a smallernumber of waveguide grating routers (WGR) 1360. The WGR 1360 nowreceives up to p signals wavelength multiplexed upon a given WGR inputchannel. Hence, a subset of the input channels of the WGR need now beused. In this manner, approximately N/p input channels of the WGR needonly be connected. Given proper selection of the wavelengths, for afully utilized WGR, all N WGR output channels will receive theappropriate signals. The subset of WGR input channels, each used tocarry p wavelength multiplexed signals are wavelength demultiplexed todistinct WGR outputs. As in FIG. 13, adjacent WGR inputs may beassociated with the various reordering buffer delay elements, resultingin the combination of these signals on a given WGR output. In thismanner, the WGR performs both a summing or combination function as wellas a wavelength demultiplexing function. The groups of k signals cover pof the overall N channels at once. It is now possible that more then onesignal is active on each of the 1.k inputs to the WGR.

[0078] The WGR wavelength steering function will ensure that thesesignals appear on distinct physical output ports. Proper wavelengthselection avoids wavelength and temporal collisions on each of the WGRoutput ports. The WGR 1360 integrates the k signals for each of thewavelength multiplexed input channels and provides a correspondingoutput for each of the output channels. The maximum port size of the WGRdictates the reduction in complexity achieved. Hence, if the number ofchannels that could be processed by a single WGR, is “W,” then, thenumber of WGRs required scales as (N×m)/W. The number of channels thatmay be processed by each WGR with a given port dimension is a functionof buffer depth “k” and the dimension of concurrency, e.g., “p” asdescribed above.

[0079] Thus, each of the N×m packet trays can be selectively timeshifted by up to k time slots. Thereafter, the wavelength of each packettray 100 is restored, amplified and converted at conversion stage 1370-iand 1380-i to a new wavelength, λ_(desired next stage), having awavelength that is appropriate for the next (switching) stage.

[0080] Applications

[0081] A technique often referred to as wavelength banding has beenproposed for future systems. In this paradigm, wavelength spacing on thenetwork connections is not equal, but allocated on a basis of how muchbandwidth a signal needs. If the multiplexer, demultiplexer block isreplaced by a banded multiplexer/banded demultiplexer block, then theOPTR would work in this context also, since all of the switching,storage, delays, signal restoration (timing)/gain/conversion is of avery broadband nature, hence the swithed packet trays could havediffering optical wavelength bandwidth requirements. At some point, thevery fast signals (today around 40 GHz) start exceeding the ITU definedwavelength spacings, so you could imagine that, for example, a 320 GHzsignal would require bandwidth that would span multiple ITU wavelengthpickets, that is those pickets would be banded together for transportand switching needs. The disclosed OPTR architecture supports such awavelength banding implementation.

[0082] In another variation, optical time division multiplexed (OTDM)signals can be accommodated within the optical tray router 200architecture. A demultiplexer would be based upon, for example, a MachZehnder interferometer or a similar device providing, techniques todemultiplex very high rate data on a single wavelength. The resultingdemultiplexed signals would be presented to the splitter 235 stage. Anew functional block would need to be added after the WDM and prior tothe Splitter 235 block for this time demultiplexing step. Similarly,prior to the O-Mux block 265, a TDM block would be added. Thus, the samearchitecture can be applied to time division multiplexed packet trays aswell as straight wavelength division multiplexed packet trays.

[0083] It is to be understood that the embodiments and variations shownand described herein are merely illustrative of the principles of thisinvention and that various modifications may be implemented by thoseskilled in the art without departing from the scope and spirit of theinvention.

I claim:
 1. A method performed by a router for routing an opticalsignal, comprising: receiving a packet tray including a plurality ofpackets, said packet tray having an associated initial wavelength; andmodifying said associated initial wavelength to control the routing ofsaid packet tray through a plurality of stages of said router.
 2. Themethod of claim 1, wherein a payload associated with said packet tray isprocessed only as an optical signal.
 3. The method of claim 1, whereinheader information associated with said packet tray is processed as anelectrical signal.
 4. The method of claim 1, wherein header informationassociated with said packet tray is processed as an optical signal. 5.The method of claim 1, wherein header information associated with saidpacket tray is processed as a hybrid of optical and electrical signals.6. The method of claim 1, further comprising the step of switching saidpacket tray received on an input channel to an appropriate outputchannel based on associated header information.
 7. The method of claim1, wherein said packet tray is multiplexed in a wavelength divisionmultiplexed system to transmit said packet tray with a plurality ofadditional packet trays on the same channel.
 8. The method of claim 1,further comprising the step of restoring said packet tray.
 9. The methodof claim 1, wherein said modifying step further comprises the step ofaligning each packet tray to a master clock-based start of packet traytemporal reference using a tunable optical delay.
 10. The method ofclaim 1, wherein said modifying step further comprises the step ofshifting one or more packet trays to avoid a collision on an outputchannel.
 11. The method of claim 1, further comprising the step ofupdating header information of said packet tray to include routinginformation for a subsequent node.
 12. The method of claim 11, whereinsaid header information is updated in an optical domain.
 13. An opticalpacket tray router, comprising: a wavelength demultiplexer forseparating a plurality of packet trays received on the same channel; aheader section for extracting header information from each packet trayand for processing said header information associated with each packettray to route each packet tray to an appropriate destination channel andto make wavelength and timing decisions; and a data section forprocessing said packet trays only in an optical domain, said datasection introducing at least one wavelength selective delay to a packettray based on said timing decisions.
 14. The packet tray router of claim13, wherein said wavelength selective delay is based on a generatedoptical control wavelength that adjusts the wavelength of a given packettray.
 15. The packet tray router of claim 14, wherein said generatedoptical control wavelength is generated by a wavelength server.
 16. Thepacket tray router of claim 14, wherein said generated optical controlwavelength is applied to a multi-wavelength Bragg grating that shiftstemporally a packet tray based on an optical control wavelength assignedto the packet tray.
 17. The packet tray router of claim 14, wherein saidgenerated optical control wavelength is applied to a dispersive mediumwhere the transmission time through the dispersive medium is a functionof an optical control wavelength assigned to the packet tray.
 18. Thepacket tray router of claim 13, wherein said wavelength demultiplexer isembodied as a banded demultiplexer to permit wavelength banding.
 19. Thepacket tray router of claim 13, wherein said wavelength demultiplexerdemultiplexes high rate data on a single wavelength in an OTDM system.20. A wavelength server that generates a plurality of optical controlwavelengths, comprising: a broadband laser source covering a wavelengthrange including said plurality of optical control wavelengths; anoptical gain stage for amplifying said laser source; at least one lensthat creates a parallel wave front; and a tunable grating array, whereineach element in said tunable grating array generates one of opticalcontrol wavelengths.
 21. The wavelength server of claim 20, wherein eachof said optical control wavelengths adjusts the wavelength of a packettray to achieve a desired routing of an optical signal.
 22. Thewavelength server of claim 20, wherein each of said optical controlwavelengths adjusts the wavelength of a packet tray to introduce awavelength selective delay.
 23. The wavelength server of claim 20,wherein said at least one lens is fabricated using a traditional opticalbench approach.
 24. The wavelength server of claim 20, wherein said atleast one lens is fabricated using a silicon optical bench approach. 25.The wavelength server of claim 20, further comprising means for couplingsaid tunable grating array to a fiber bundle array.
 26. A method forgenerating a plurality of optical control wavelengths, comprising:generating a laser source signal covering a wavelength range includingsaid plurality of optical control wavelengths; amplifying said lasersource signal; creating a parallel wave front in said laser sourcesignal; and applying said laser source signal to a tunable gratingarray, wherein each element in said tunable grating array generates oneof optical control wavelengths.
 27. The method of claim 26, wherein eachof said optical control wavelengths adjusts the wavelength of a packettray to achieve a desired routing of an optical signal.
 28. The methodof claim 26, wherein each of said optical control wavelengths adjuststhe wavelength of a packet tray to introduce a wavelength selectivedelay.
 29. The method of claim 26, wherein said parallel wave is createdusing at least one lens fabricated using a traditional optical benchapproach.
 30. The method of claim 26, wherein said parallel wave iscreated using at least one lens fabricated using a silicon optical benchapproach.
 31. The method of claim 26, further comprising the step ofcoupling said tunable grating array to a fiber bundle array.
 32. Amethod for processing an optical signal in a multi-stage network node,comprising: converting a wavelength of said optical signal to an opticalcontrol wavelength appropriate for a current stage using a tunablecontinuous wave light received from a wavelength server; processing saidoptical signal in an optical domain using a passive device; andconverting a wavelength of said optical signal to an optical controlwavelength appropriate for a subsequent stage using a tunable continuouswave light received from a wavelength server.
 33. The method of claim32, wherein said converting steps further comprise a restoration of saidoptical signal.
 34. The method of claim 32, wherein said processing stepimplements a switching function.
 35. The method of claim 32, whereinsaid processing step implements an alignment function.
 36. The method ofclaim 32, wherein said processing step implements a multiplexingfunction.
 37. The method of claim 32, wherein said processing stepimplements a delay function.
 38. An optical signal processor in amulti-stage network node, comprising: a wavelength converter forconverting a wavelength of said optical signal to an optical controlwavelength appropriate for a current stage using a tunable continuouswave light received from a wavelength server; a passive device forprocessing said optical signal in an optical domain; and a wavelengthconverter for converting a wavelength of said optical signal to anoptical control wavelength appropriate for a subsequent stage using atunable continuous wave light received from a wavelength server.
 39. Theoptical signal processor of claim 38, wherein said wavelength convertersare further configured to restore said optical signal.
 40. The method ofclaim 38, wherein said passive device implements a switching function.41. The method of claim 38, wherein said passive device implements analignment function.
 42. The method of claim 38, wherein said passivedevice implements a multiplexing function.
 43. The method of claim 38,wherein said passive device implements a delay function.